This invention relates to a liquid crystal optical device, and more particularly to a liquid crystal optical device having a high-speed response characteristic which utilizes an optically active nematic liquid crystal composition capable of dielectric relaxation at a low frequency.
The driving method for driving a liquid crystal optical device utilizing a liquid crystal panel including an optically active nematic liquid crystal composition exhibiting dielectric relaxation at low frequencies is described generally in Japanese patent application No. 55-141,085, corresponding to U.S. application Ser. No. 309,521, assigned to the assignee of this application and which application is incorporated herein by reference, and No. 56-7043 and No. 56-7047. Switching of the device is performed by applying signals of two frequencies, a low frequency and a high frequency, to the liquid crystal composition for producing dielectric relaxation. In the conventional techniques, the response speed of the liquid crystal can be increased to a certain extent. However, the response speed is limited in several milliseconds to 10-odd milliseconds. U.S. Pat. No. 3,857,629 is illustrative of such an optical device and increasing response times is described generally in C. S. Bak, K. Ko and M. M. Lakes, Fast Decay In A Twisted Nematic Induced by Frequency Switching, J. of App. Physics, Vol. 46, No. 1, January, 1975. Nonetheless, it would be desirable to improve the driving methods disclosed in these publications, in particular the response speed of the liquid crystal composition.
Accordingly, it is desirable to provide a liquid crystal optical device capable of operating at higher response speeds which will permit such liquid crystal optical devices to find wider application in high-speed printing devices, and the like.